As illustrated in FIGS. 1A, 1B and 2, a plastic encapsulated power IC package includes a silicon die 10, die attachment 20, passivation 30, wire interconnects 40, a lead frame 50, and plastic molding compound 60. This package is often used in automotive electronics and typically operates in a severe thermal environment.
The thermal expansion mismatch of different materials produces thermal stresses along the adhesion interface between the materials during the cooling process and during low temperature thermal cycling. In traditional plastic encapsulated IC packages, there is a sharp, angular edge at the interface between the molding compound 60 and the lead frame 50. The sharp corner of the edge causes a stress concentration which, in turn, causes crack initiation at the interface between the molding compound 60 and the lead frame 50. Such cracks in the molding compound comprise a significant reliability issue for any power IC operated in such a harsh, thermally-cycled environment.